Apparatus for desalination and purification of water by reverse osmosis and ultrafiltration

ABSTRACT

An apparatus for desalination and purification of water by reverse osmosis and ultrafiltration. Such apparatus require seals at the individual modular elements between the untreated water passages and the permeate-withdrawal passages. These seals comprise two sealing rings which are essentially U-shaped, are of similar but inverted shape, and are made of synthetic material having a limited flexibility. Pairs of the sealing rings sealingly abut one another in the central plane of the modular guide plate via respective ones of their arms which extend essentially radially. The second, outward disposed arms sealingly contact an adjacent diaphragm. Disposed on the outer surface of the portion which connects the arms are channels for the withdrawal of the permeate.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for desalination andpurification of water by reverse osmosis and ultrafiltration, whichapparatus comprises: plate-like carrier plates and water-guiding plateswhich are stacked alternately one upon the other and are secured betweentwo end plates; ring-shaped diaphragms which are disposed between thecarrier plates and the water-guiding plates and are lined with a filtersheet, with untreated water flowing over the diaphragm side of a givendiaphragm, and permeate being withdrawn from the filter side thereof;and sealing arrangements disposed at the periphery of each water-guidingplate between untreated-water passages and permeate-withdrawal passages;beyond the edges of the guide plates, the carrier plates rest upon oneanother via a widened edge portion, and form, via a gap produced by areduced thickness of the edge portions of the carrier plates, apermeate-withdrawal passage which communicates with the filter sheets ofthe diaphragms.

Apparatus of the aforementioned type, as they are disclosed, forexample, in the U.S. Pat. No. 4,228,014, which belongs to the Assigneeof the present application, must be serviced at regular intervals; inother words, the apparatus must from time to time be provided with newdiaphragms, or at least the diaphragms must be freed of deposits, suchas algae, sewage, and the like. Since such servicing always involves (atleast partial) interruption of operation, it is essential that theapparatus for desalination and purification of water not only be capableof being rapidly disassembled, but also be capable of again being veryrapidly reassembled without any alignment and sealing errors. Up to now,this reinstallation has been extremely time consuming and involved a lotof work, since the seals which were used were always multi-part and alsowere made of different materials. U-shaped edge seals for thewater-guiding plates had to be laboriously placed on the toothed rim ofthe water-guiding plates, and holding rings or water-guiding rings alsohad to be inserted, on the one hand to hold the annular diaphragms andfilter sheets in position, and on the other hand to also support thecarrier plate seals on the periphery, so that the latter cannot shiftout of position when the untreated-water stream is redirected in theregion of the edges of the guide plates.

It is therefore an object of the present invention to provide forapparatus of the initially mentioned type an improved peripheral sealwhich permits assembly of a modular stack to be carried out considerablymore easily and rapidly.

SUMMARY OF THE INVENTION

To realize the aforementioned object, the apparatus of the initiallydescribed type is inventively embodied in such a way that the individualsealing arrangements comprise two symmetrical, i.e. of similar butinverted shape, sealing rings which are essentially U-shaped and aremade of synthetic material having a limited flexibility; pairs of thesesealing rings sealingly abut one another in the central plane of theguide plate, radially outwardly of the periphery of the latter, viarespective ones of their arms, which extend essentially radially;outwardly disposed second arms of the sealing rings sealingly contact anadjacent diaphragm, with the outer surface of that portion of thesealing ring which connects the arms being provided with channels forthe formation of the permeate withdrawal passage.

The inventively provided U-shaped sealing rings now have no connectionwhatsoever with the guide plate, which is centrally disposed between thesealing rings and can have untreated water flowing therearound. At thesame time, the two outer arms of a given pair of sealing rings abutagainst two opposed diaphragms, so that the untreated water is reliablyseparated from the permeate-withdrawal passages. Due to the flexiblenature of the synthetic material, the two adjacent arms of a given pairof sealing rings sealingly abut one another in the central plane of theguide plate, and actually beyond the guide plate itself. By using only asingle sealing material, and a single shape for the sealing ring, therenaturally also results a considerable savings in cost.

Pursuant to specific features of the present invention, the sealingrings may be shaped in such a way that in a state of rest their armsdiverge from one another. The outer side of that arm of a given sealingring which faces the central plane of the guide plate may be providedwith a planar surface and with a rounded edge. The outer side of thatarm of a given sealing ring which faces the diaphragm may be providedwith a sealing rib which extends all the way around. This sealing ribmay have a height of less than 1 mm, and may have a rounded-off,triangular cross-section at its tip.

The material of the sealing rings may be resistant to acids andalkalies, and may be a synthetic material which is compatible withfoodstuffs. Examples of synthetic materials include polypropylene,polyvinylidene fluoride (PVDF), or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of the present invention is describedsubsequently with the aid of the drawings, which show;

FIG. 1 a radial section through an apparatus for desalination andpurification of water pursuant to the state of the art of U.S. Pat. No.4,228,014,

FIG. 2 an enlarged partial cross-section of the apparatus of FIG. 1through the edges of an end plate and an adjacent carrier plate;

FIG. 3 an illustration similar to that of FIG. 2 showing an inventivesealing arrangement which replaces the sealing arrangement of FIGS. 1and 2; and

FIG. 4 an even greater enlargement of an axial partial view of aninventive sealing ring.

DESCRIPTION OF PREFERRED EMBODIMENTS

With the aid of FIGS. 1 and 2, there will first be described anapparatus for desalination and purification of water by reverse osmosisand ultrafiltration as disclosed in applicant's U.S. Pat. No. 4,228,014.

The apparatus of FIG. 1 comprises two end plates 10 and 20 which haverelatively thick walls. Disposed between these end plates 10 and 20 arecarrier plates 30 and guide plates 40, which are preferably made ofsynthetic material and are disposed in such a way that they arealternately stacked. Outer seals 50 and inner seals 60 are provided onthe guide plates. Disposed on opposite sides of the carrier plates aremembranes or diaphragms 70 which are lined with filter sheets. Holdingrings 80 serve as radial outer boundaries for the guide plates 40 andtheir outer seals 50. A plurality of clamping bolts are provided to holdthe stack of plates together; these clamping bolts are disposed aroundthe periphery of the stack of plates, and are anchored in the end plates10 and 20. Provided in the middle of the end plates 10 and 20, which arepreferably in the form of circular disks, is a central opening 11through which the untreated water which is to be desalinated isconveyed; by way of example, in the drawing this occurs in the directionof the indicated arrows. One or more radially directedpermeate-withdrawal passages 12 are provided in the end plates 10 and20. These passages 12 open into an axially directed permeate-withdrawalpassage 13 which is disposed radially outwardly of the holding rings 80.

If the apparatus as a whole is disposed in a collecting tank, thepassage system 12, 13 can, of course, be eliminated. In this case, thepermeate at the outer periphery of the stack of plates can drain off viaappropriate outlet gaps. The carrier plates 30 are provided with aplanar parallel edge portion 31, the axially directed end faces of whichrest sealingly against one another or against the inside surfaces of theplates 10 and 20. To effect sealing, an O-ring 32, which extends allaround, is disposed in one of the axially directed end faces of the edgeportion 31. Provided in the carrier plates 30 inwardly of this O-ring 32are axial passages 33 which during assembly are aligned with the axialpassage 13 of the end plates. That portion of the carrier plate 30adjacent to the passage 33 has a somewhat smaller thickness, so thatwhen the carrier plates are stacked, gaps result via which the permeatecan reach the axial passage 33 (or a tank which surrounds the stack ofplates) in a manner which will subsequently be described in greaterdetail. The axial thickness of the carrier plate 30 is reduced towardthe middle to an annular flange or collar 36, so that the spacingbetween adjacent carrier plates becomes continuously greater towards themiddle in this region. The inclined wall portions of the carrier plate30 form a support for the circular diaphragms 70, which are lined with afilter sheet. The annular collars 36 are disposed directly next to acentral opening 37 of the carrier plates 30. This opening 37 is alignedwith the central opening of the end plates 10 and 20. The guide plates40 are disposed in the disk-shaped space between the individual carrierplates or between the outermost carrier plates and the correspondinglyrecessed adjacent surfaces of the end plates 10 and 20; over a largeannular portion thereof, the guide plates 40 have substantially parallelwalls. The guide plates have a thinner central portion 41 which passesthrough the central openings 11, 37, so that cylindrical borecompartments or sections 42 result in these central openings.

Disposed on the outer edge of the guide plates 40 are notches 44 betweenwhich tooth portions remain. These tooth portions carry a U-shaped ringseal 50, which extends over the individual teeth only to such an extentthat portions of the notches form passages between the two sides of theguide plates. It should be noted that the outer U-shaped guide plateseals 50 rest against adjacent carrier plates.

Disposed in each of the aforementioned cylindrical compartments of thecentral opening are two L-shaped sealing rings 61 and 62, by means ofwhich the diaphragms 70 are also held on the carrier plates 30.

The annular disk-like diaphragms 70 extend in the radial direction fromthe annular collar 36 to the inner periphery of the holding rings 80.The permeate which has passed through the diaphragm 70 can, below theU-shaped seal 50, reach the step surface of the carrier plate 30. Sothat from this step surface the permeate can now reach the axialpassages 33 or 13, and hence the permeate-withdrawal passages 12, theholding rings 80 are provided at their radially outwardly disposedperipheral surface with fine channels, which are preferably produced byknurling.

From the above description of the heretofore known apparatus fordesalination and purification of water, it can be seen that theuntreated water which enters at the bottom end of the central opening 11can flow radially through the stack of plates in a zig-zag fashion. Theuntreated water initially flows from a central portion 41 of the guideplate radially outwardly along the latter, then flows to the oppositeside of the guide plate at the notches 44, and then again flows radiallytoward the middle to reach the next cylindrical compartment 42. At theend of the filter process, the nondesalinated or nonpurified, and henceconcentrated, residual water is again discharged at the upper end of thecentral opening 11. The permeate collects below the diaphragms in thefilter sheets, and passes around the holding rings 80 to the carrierplate gaps and to the permeate discharge 13-12.

From the foregoing description it was clear that the U-shaped seals 50,which are placed upon the teeth at the periphery of the guide plates,have the task of pressing against the diaphragms 70 and the filtersheets, and of holding them in their position. Assembly is made moredifficult by the fact that that edge of the guide plate which isprovided with the U-shaped seal 50 must be placed exactly in the centralopening of the thin holding ring 80. In order to get by without thiscomplicated assembly, and in order to reduce the cost of the entiresealing arrangement, it is proposed pursuant to the present invention toreplace the previously described seals 50 with the sealing rings 100which are illustrated in FIGS. 3 and 4; these sealing rings 100furthermore undertake the function of the holding rings 80.

As shown in FIGS. 3 and 4, U-shaped sealing rings 100 are now used. Ateach location, two of these sealing rings 100 work together as a pairand surround a guide plate 40 which is disposed centrally between thesealing rings, but is not contacted by them. Each sealing ring 100 has aU-shaped cross-sectional profile. The outer diameter of each sealingring 100 is such that the sealing rings can be placed into the recess ofthe carrier plates 30 similar to the previously used holding rings 80.During assembly, an annular diaphragm 70, which is lined with a filtersheet, is first placed into the recess of the carrier plate 30 exactlyas was previously done; the diaphragm can then be held in place byinserting the sealing ring into the recess of the plate 30. Due to theelasticity of the material, a sealing ring 100 is held securely in itsrecess. The long arm 130 of the sealing ring is directed outwardly withslight prestress; the nose 131 of the long arm 130 extends over theperiphery of the latter and contacts the surface of the diaphragm 70, sothat the untreated water which flows around the guide plate 40 cannotreach the permeate-withdrawal passage. From the region below thediaphragm 70, the permeate which passes through this diaphragm can enterthe space disposed in the recess of the plate 30 radially outwardly ofthe sealing nose 131. As shown in FIG. 4, provided at this location areradial, slightly diverging channels 111 which make it possible for thepermeate to flow to the outer periphery of the sealing ring 100, wherefurther channels 112 are provided which make it possible for thepermeate to flow through the gap between two adjacent carrier plates 30.

When a carrier plate 30 is lined with a filter sheet and diaphragm 70,and is provided with a sealing ring 100, it is possible, as shown inFIG. 3, to freely place the guide plate 40 in the central portion of thesealing ring 100 inwardly of the short arm 140 thereof. Whensubsequently a further carrier plate 30 prepared in the same manner isinserted, the two similarly slightly prestressed outer ends of the shortsealing ring arm 140 abut one another (at 141) and thus assure acomplete sealing-off of the untreated water passage outwardly of theguide plate 40. Small recesses 113 which extend over the periphery areprovided at the base or connecting portion 120 of the sealing rings;these recesses give the sealing rings a greater elasticity. Theintermediate space, which is disposed between two adjacent sealing rings100 and extends over the periphery, serves the same purpose and alsoserves to improve the flow or discharge of permeate.

The material of the sealing ring is preferably synthetic material whichis compatible to, i.e. safe for use with, foodstuffs, with examples ofsuch material being polypropylene, polyvinylidene fluoride (PVDF), andthe like.

What we claim is:
 1. An apparatus for desalination and purification ofwater by reverse osmosis and ultrafiltration, comprising: plate-likecarrier plates and water-guiding plates which are stacked alternatelyone upon the other, and are secured between two end plates, with each ofsaid guide plates having a central plane; ring-shaped diaphragms whichare disposed between said carrier plates and said guide plates and arelined with respective filter sheets, with untreated water flowing overthe diaphragm side of a given diaphragm, and permeate being withdrawnfrom the filter side thereof; and a respective sealing arrangementdisposed at the periphery of each guide plate between untreated-waterpassages and permeatewithdrawal passages; beyond the edges of said guideplates, said carrier plates rest upon one another via a widened edgeportion and form, via a gap produced by a reduced thickness of the edgeportions of said carrier plates, a permeate-withdrawal passage whichcommunicates with said filter sheets of said diaphragms;the improvementwherein individual ones of said sealing arrangements comprise a pair ofsymmetrical sealing rings which are essentially U-shaped and are made ofsynthetic material having a limited flexibility; each of said sealingrings has a first essentially radially extending arm directly towardsaid guide plate, a second essentially radially extending arm directedtoward a respective one of said diaphragms, and a connecting portion,remote from said guide plate, which interconnects said first and secondarms; for a given pair of sealing rings, said first arms are remote fromone another, and said second arms sealingly abut one another in saidcentral plane of a given guide plate radially outwardly of the peripheryof the latter, with said first arms sealingly contacting an adjacentdiaphragm; the outer surface of said connecting portions, remote fromsaid guide plates, is provided with channel means to form part of saidpermeate-withdrawal passages.
 2. An apparatus according to claim 1, inwhich each of said sealing rings is formed in such a way that in a stateof rest, said first and second arms thereof diverge from one another. 3.A apparatus according to claim 2, in which that surface of each of saidfirst arms of said sealing rings remote from said second arm thereof isplanar and has a rounded-off edge.
 4. An apparatus according to claim 3,in which that surface of each of said second arms of said sealing ringswhich faces said diaphragm is provided with a sealing rib which extendsall the way around.
 5. An apparatus according to claim 4, in which saidsealing rib extends less than 1 mm from the surface of said second arm,and has a triangular cross-section, the tip of which is rounded off. 6.An apparatus according to claim 5, in which the material of said sealingrings is resistant to acids and alkalies.
 7. An apparatus according toclaim 6, in which the material of said sealing rings is syntheticmaterial which is safe for use with foodstuffs.
 8. An apparatusaccording to claim 7, in which said synthetic material is selected fromthe group consisting of polypropylene and polyvinylidene fluoride(PVDF).